Analytical Solution for the Chloride Diffusivity of Hardened Cement Paste

Due to its importance to the durability assessment and design of reinforced concrete structures located in a marine or deicing salt environment, it is essential to determine the chloride diffusivity of hardened cement paste. This paper presents an analytical solution for the chloride diffusivity of hardened cement paste. By modeling hardened cement paste as a two-phase composite material, composed of gel and capillary pores and solid cement gel, an analytical solution is derived for the chloride diffusivity of hardened cement paste based on the general effective medium theory. A parameter involved in the analytical solution is then determined by experimental calibration. After verifying the analytical solution with experimental results obtained from the literature, the effects of the water/cement ratio and the degree of hydration on the chloride diffusivity of hardened cement paste are evaluated in a quantitative manner. It is found that the chloride diffusivity of hardened cement paste with a water/cement ratio of 0.7 is three orders of magnitude larger than that with a water/cement ratio of 0.3 and that the extent to which the degree of hydration influences the chloride diffusivity of hardened cement paste is in the range of 50 to 80% when the degree of hydration varies from 0.5 to 1.0. The paper concludes that the analytical solution presented in the paper can predict the chloride diffusivity of hardened cement paste with reasonable accuracy.